1. Field of the Invention
The present invention relates to a mounting device which is provided with a vibration control function and used to mount an engine, for example, a power unit including an internal combustion engine, a speed change gear, etc., for a motor vehicle, or other machine operated by a motor, to a vehicle body. More particularly, the present invention relates to a liquid-sealed mounting device in which an incompressible liquid is sealed.
2. Related Art
A known liquid-sealing device includes two liquid chambers provided, orifices provided between the two liquid chambers, a partition wall part provided between the two liquid chambers and composed of a flexible or mobile vibration-absorptive member, and an electromagnetic actuator. The electromagnetic actuator vibrates the vibration-absorptive member at the same frequency as the vibrations of an engine and in a phase opposite to the vibrations of the engine so as to have a vibration isolating function (as disclosed in Japanese Examined Utility Model Publication No. 4-39481 and Japanese Examined Patent Publication No. 4-59495).
Such a known mounting device has the following problem. Because vibrations at various frequencies occur in the engine of a motor vehicle, which operates in states ranging from idling to acceleration not to mention normal operation, the vibrations of the engine have to be attenuated and cut off according to the operational condition by always keeping the electromagnetic actuator in operation. As a result, the operation ratio of the electromagnetic actuator is so high that breakdown or shortening of its service life occurs, and the power consumed by the electromagnetic actuator is quite large.
In addition, in order to provide a mounting device which has the ability to vary the frequency of vibration, by closing a part of the orifice with a control valve when the engine is idling, for example, it becomes necessary to provide an actuator for the control valve opening or closing the orifice in addition to the actuator for the vibration-absorptive member. As a result, the number of parts and components increases and the device becomes large in size.